1. Field of the Invention
The present invention generally relates to an index or ratchet shifter for a bicycle transmission. The index shifter includes a casing or housing which encircles the handlebar of a bicycle and is fastened thereto, and a locking ring having notches, which locking ring is rotationally mounted in the casing and is equipped with an actuating pull or cable for actuating the bicycle transmission. The index shifter also has a detent spring including a lug and two feet, whereby the detent spring is arranged in a ring-shaped recess in the casing between a first sidewall and a second sidewall.
2. Background Information
European Patent No. 676 325 A2 discloses a ratchet or index shifter which, as shown in FIG. 1, is based on the prior art and includes a detent spring located a fixed casing and a rotary locking ring. The detent spring is generally arranged in a ring-shaped recess in the casing, which recess has two sidewalls. One or the other of these sidewalls is contacted by the detent spring as a function of the direction of rotation of the rotary locking ring. This detent spring is carried by a lug which engages in notches in the locking ring and which lug of the detent spring is braced against the notches by spring force. Because the ring-shaped recess in the casing has a span slightly greater than the length of the spring, the spring can be moved back and forth within the ring-shaped recess. This back and forth motion is equivalent to overshift in one direction, which with a derailleur gear shifting system results in shifting from a small sprocket to the next larger one.
If such an index shifter is used to actuate a bicycle transmission, in particular a gear hub, much shorter and very accurate overshifts are required, however. Because the known detent spring disclosed in European Patent No. 676 326 A2, like the detent spring in accordance with the present invention, is shaped similar to a coat hanger, the length of the spring and thus the overshift available at the moment changes as the spring deflects when passing through the interval between two notches in the locking ring. To eliminate the extension of the spring due to deflection, and thus prevent this function from resulting in changes to overshift, the stops to limit spring travel should be located somewhere other than at both ends of the ring-shaped recess.
The present invention therefore teaches that one sidewall of the ring-shaped recess can be used as a limit stop for the spring, and also that there is a casing projection between the feet at the underside of the spring, which casing projection, together with one of the feet, can form the second limit stop. This results in a shift play or clearance, which shift play can be dimensioned as desired and, most importantly, which shift play does not change during the shift process.